1. Field of the Invention
This invention relates to a high efficiency thermal head to be used for a thermal printer and a method for manufacture of the thermal head.
2. Description of the Related Art
Generally as shown in FIG. 9, a conventional thermal head is provided with a glaze thermal insulation layer 102 formed of alumina having a thickness of approximately 80 μm formed on the top face of a radiative substrate 101 and a convex 102a having a height of approximately 5 μm formed by means of the photolithographic technique on the top face of the glaze insulation layer 102.
Furthermore, a heating resistor 103 formed of Ta—SiO2 is formed on the top face of the glaze thermal insulation layer 102 by means of the sputtering technique and photolithographic technique so as to form a pattern. Furthermore, a part of the heating resistor 103 functions as a heating element 103a arranged at an equal intervals on the space between a common electrode 104a and an individual electrode 104b, which will be described hereinafter.
Herein, a heating resistor that has been subjected to high temperature stabilization heat treatment at 500 to 800° C. after film forming is used as the heating resistor 103. The high temperature stabilization heat treatment of the heating resistor 103 brings about the improved characteristic of the heating resistor 103 so that heating in printing does not result in increased resistance loss, and so that a heating head prints without irregular printing density.
Therefore, the high temperature stabilization heat treatment of the heating resistor 103 is required inevitably for the conventional thermal head.
Furthermore, on the top face of the heating resistor 103, a power supplier (which includes the common electrode 104a and the individual electrode 104b) that functions to supply electric energy to the heating resistor 103 having a thickness of approximately 2 μm consisting of a metal material such as Al, Cu, or Au is formed by means of sputtering, and the common electrode 104a, the individual electrode 104b, and outside-connection terminals (not shown in the drawing) of the electrodes 104a and 104b are formed by means of the photolithographic technique.
Furthermore, at least on the top faces of the heating resistor 103 and the power supplier, a protection layer 105 that functions to prevent wearing and oxidation of the heating resistor 103 and the electrodes 104a and 104b is formed.
The protection layer 105 is formed of a layer having a thickness of approximately 5 to 10 μm consisting of hard ceramic such as Si—O—N or Si—Al—O—N formed by means of sputtering.
In the case of the conventional thermal head, a current is supplied selectively to the common electrode 104a and individual electrode 104b to heat the heating element 103a so as to transfer ink of an ink ribbon onto plain paper and so as to print a desired character or a desired image. Otherwise, a desired character or a desired image is printed directly on heat sensitive paper.
A thermal printer having a conventional thermal head as described hereinabove that is portable and driven by use of a battery has been available commercially. The thermal head of the portable printer as described hereinabove is the biggest power consumer, and it particularly causes the short life of a battery. A power-saving thermal head has been expected to be developed.
However, in the possible case where the thermal efficiency of a conventional thermal head is improved to save power by reserving the heat of the glaze thermal insulation layer 102 formed of glass glaze, the film thickness of the glaze should be thick. However, formation of a glaze thermal insulation layer 102 having a thickness thicker than conventionally used 80 μm is difficult technically and the thickness is limited by the film forming technique used. As the result, no power-saving thermal head has been developed.
Furthermore, a high temperature stabilization heat treatment at a temperature of 500 to 800° C. is required to obtain a conventional thermal head after a heating resistor 103 is molded. However, the thermal treatment results in a complex manufacturing process. Furthermore, the thermal treatment requires calcination equipment, which results in high cost.